Various techniques have been developed for the recovery of oil from oil shale and, expressed simplistically, the basic requirement is that the shale be heated to a level (in the order of 550.degree. C.) at which the shale releases its gaseous and liquid products. Designing a retort to meet this fundamental requirement as such does not present a significant problem but, in order that a shale oil recovery process might be worked in a manner which compares favourably in economic terms with the more conventional oil producing processes, the retort must be capable of providing a high throughput. This, in turn, requires a substantial heat input and the viability of shale oil production is dependent largely on achieving efficient utilization of energy input.
One approach which has been proposed for the heating of feed shale involves crushing of the shale to particulate size and contacting it in a fluidized reaction bed with spent shale which has been heated to an appropriate level, using a convenient fuel such as the residual carbon in the shale. The kerogen content of the feed shale is converted to gas and oil vapour products in the fluidized bed as a result of heat exchange between the feed shale and the heated (heat medium) shale.